1. Field of the Invention
The present invention relates to driving LED (Light-Emitting Diode) lamps and, more specifically, to controlling the current supplied to the LED lamps.
2. Description of the Related Arts
LEDs are being adopted in a wide variety of electronics applications, for example, architectural lighting, automotive head and tail lights, backlights for liquid crystal display devices, flashlights, etc. Compared to conventional lighting sources such as incandescent lamps and fluorescent lamps, LEDs have significant advantages, including high power efficiency, good directionality, color stability, high reliability, long life time, small size, and environmental safety. Because of advantages over incandescent lamps, particularly the power efficiency (lumens per watt) and spectral quality, use of LED lamps rather than incandescent lamps is expected to increase. Additionally, LED lamps have lower environmental impact than fluorescent lighting systems (fluorescent ballast combined with fluorescent lamp), which that may cause mercury contamination during fluorescent lamp disposal.
However, while conventional incandescent lighting systems are voltage driven devices, LED lamps are current-driven devices. Hence, conventional LED lamps cannot be direct replacements of incandescent lamps and fluorescent systems without modifications to current wiring and component infrastructure. Because LED lamps are current driven, different techniques for controlling them are required.
Conventional techniques for regulating current used to drive LED lamps use an output current sensing resistor or a transformer. However, use of an output current sensing resistor causes power loss, while use of a current transformer increases overall system cost. Additionally, conventional techniques monitor the current driving a LED lamp and the output voltage to prevent voltage overshoot and protect the LED lamp by using a separate sets of components, further increasing system complexity.